This proposal continues and enhances the existing New Vaccine Surveillance Network (NVSN) site in Rochester, NY. The over-arching goal is to inform the nation about the burden of vaccine-preventable diseases (VPDs) and the impact of new vaccines and vaccine policies. Our Rochester NVSN site (a founding NVSN member), has been a leader in shaping all aspects of the NVSN including population-based surveillance for new or upcoming vaccines, vaccine effectiveness (VE) studies, refinement of laboratory methods, health services and epidemiologic studies, and dissemination of findings. Our proposal focuses activities on acute gastroenteritis (AGE) in young children (rotavirus, norovirus), but has equal strength in studying a variety of acute respiratory infections (ARIs). We have the infrastructure and comprehensive expertise to begin all activities on day 1. The specific aims are to (A) operate a population-based NVSN site to collect epidemiological, clinical, and vaccination data on cases and healthy controls, and (B) conduct a spectrum of NVSN activities-- (B1) conduct enhanced, year-round surveillance for AGE in hospital and emergency department (ED) settings for children <11y and assess population-wide disease burden; (B2) evaluate rotavirus VE annually; (B3) collect AGE surveillance data from healthy controls to better define the disease burden; and (B4) perform a variety of optional studies to better understand VPDs and the impact of vaccines. We propose 8 possible optional studies, all of which we can perform depending on NVSN funding and priorities. Three high- priority optional studies (which we can perform within the Year-2 budget) include: (B4a) a cohort study to evaluate the incidence, burden and transmission of AGEs and ARIs; (B4b) a study to measure the cost of AGE-related hospitalizations and ED visits; and (B4c) ARI surveillance to assess the burden of RSV and parainfluenza and the potential for new ARI vaccines (RSV and parainfluenza) and also to provide ARI controls for our AGE-focused surveillance. Our NVSN has experienced personnel, accurate laboratory and surveillance techniques, and outstanding epidemiologic and health services research capabilities. We have full access to all hospital and ED databases to complement surveillance activities. Our community is unique in the US in our outstanding collaboration with primary care practices including access to virtually all practices in the county for vaccination data and the potential for population-based outpatient surveillance. This proposal will provide critical information to develop sound polices consistent with national goals to preventing VPD in children.